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Peer Review | Position Paper
Carbohydrates in sports nutrition
Position of the working group sports nutrition of the German Nutrition
Society (DGE)
Daniel König, Hans Braun, Anja Carlsohn, Mareike Großhauser, Alfonso Lampen, Stephanie Mosler,
Andreas Nieß, Helmut Oberritter, Klaus Schäbethal, Alexandra Schek, Peter Stehle, Kiran Virmani,
Rainer Ziegenhagen, Helmut Heseker
Abstract Introduction
Carbohydrates are an important source of energy during physical exer- Among macronutrients, carbohydrates are
cise. Carbohydrates lead to a higher energy yield and higher energy flux particularly important for athletic performance
per liter of oxygen than the oxidation of fatty acids. However, the storage [1]. Carbohydrates have a very high energy
capacity for carbohydrates in liver and muscles is limited. Therefore, en- efficiency and can be metabolized both aerobi-
durance athletes should include a high proportion of carbohydrates in cally and anaerobically [2]. Particularly when
their daily diet. The individual amount depends on body weight and the oxygen uptake is considered, which is particu-
extent of physical activity. Energy expenditure during physical exercise larly important in endurance sports, the en-
results in a gradual depletion of carbohydrate stores. The extent to which ergy yield in terms of the amount of adenosine
carbohydrate stores are depleted is dependent on the duration and inten- triphosphate (ATP) per liter of oxygen is higher
sity of exercise. Therefore, in particular during prolonged intense exercise, for carbohydrates than for fatty acids [3].
performance may be improved by consuming an adequate amount of
carbohydrates during exercise. In addition, following a long period of in- The total energy yield during anaerobic (2 Mol
tensive physical activity, rapid post-exercise intake of carbohydrates can ATP/Mol glucose) and aerobic (36 Mol ATP/
help replenish carbohydrate stores more quickly. Mol glucose) glucose metabolism is less than
This position paper sets out current guidelines for the type, amount and for the metabolism of fatty acids (e.g. 122
timing of carbohydrate intake in sport. It will also discuss the significance ATP/Mol stearic acid), but the flux of energy,
of “carbohydrate loading”, the glycemic index, and training without prior i.e. the ATP yield per unit of time is much
intake of carbohydrates. higher for carbohydrates [4].
Keywords: carbohydrates, position statement, sports nutrition, glycogen
stores, energy supply Compared to energy yield from fatty acids,
ATP resynthesis/unit of time is twice as high
for aerobic metabolism of glucose. In the case
of anaerobic metabolism of glucose, this value
is actually four times higher [5].
Therefore, it has been shown that a high pro-
portion of carbohydrates in the diet can signif-
icantly improve physical performance during
prolonged, intense physical exercise [6]. Fur-
thermore, there is increasing evidence that the
level of carbohydrate stores in the liver and
muscles affects training-induced adaptation
Citation processes in the body [1, 7, 8].
König D, Braun H, Carlsohn A, Großhauser M, Lampen A, Mosler
S, Nieß A, Oberritter H, Schäbethal K, Schek A, Stehle P, Virmani K, The importance of carbohydrate intake for
Ziegenhagen R, Heseker H (2019) Carbohydrates in sports nutri- athletic performance will be demonstrated
tion. Position of the working group sports nutrition of the German below with reference to the following aspects:
Nutrition Society (DGE). Ernahrungs Umschau 66(11): 228–235 - Carbohydrates in the period before physical
This article is available online:
DOI: 10.4455/eu.2019.044 exercise
- Carbohydrates during physical exercise
Peer-reviewed - Carbohydrates in the period immediately
reviewed during preparation after physical exercise
Ernaehrungs Umschau international | 11/2019
228
Carbohydrate Exercise intensity Intake level
consumption
low low intensity 3–5 g/kg BW/d
moderate moderate exercise 5–7 g/kg BW/d
(approx. 1 hour of moderate training per day)
high competitive endurance training 6–10 g/kg BW/d
(moderate to high-intensity training for 1–3 hours per day)
very high extreme training exercise 8–12 g/kg BW/d
(moderate to high-intensity training for 4–5 hours per day)
Tab. 1: Daily in take for carbohydrates in dependence of exercise intensity [1]
d = day; BW = body weight
Carbohydrates in the period prior to exercise training sessions, there are currently various
concepts for modifying carbohydrate intake
Daily nutrition with the aim of potentially improving perfor-
The basis of the athlete’s diet is food that provides all necessary mance. One of the most topical at the moment
nutrients in accordance with the food-based dietary guidelines of is training with low glycogen stores (“train
the German Nutrition Society (Deutsche Gesellschaft für Ernährung, low”) to improve fat oxidation ( see also
DGE) [9, 10]. One of the key reasons for the focus on carbohy- “Position statement of the working group
drates in the basic diet of endurance athletes is the fact that car- sports nutrition of the German Nutrition Soci-
bohydrates are optimal for restoring glycogen stores in the liver ety (DGE): Fats in sports nutrition” [15]) [14,
and muscles [1, 11, 12]. Muscle biopsy studies have shown that 16, 17].
a high proportion of carbohydrates in the diet is also associated
with high hepatic and muscular glycogen stores. In addition, the Glycogen availability is very likely modulated
level of glycogen stores correlated relatively closely with the sub- by signaling proteins that are activated by
sequent duration of exercise in endurance tests to exhaustion [6]. physical training such as AMP-activated pro-
tein kinase (AMPK) or p38 mitogen-activated
Compared to fat stores in the human body (approx. 80,000– protein kinase (MAPK) [1, 18]. Both AMPK
100,000 kcal), glycogen stores in the muscles (approx. 1,230– and MAPK are involved in the regulation of
2,050 kcal) and the liver (approx. 410 kcal) are limited. If gly- the expression and activity of transcriptors
cogen stores are depleted, energy can no longer be provided by and transcriptional coactivators, which influ-
carbohydrates. Consequently, because the ATP yield per unit of ence mitochondrial biogenesis and therefore
time is smaller for the oxidation of fatty acids (see above), exercise oxidative capacity [19].
intensity must be reduced. Although many studies have demonstrated
The rate of glycogen depletion depends on the duration and inten- an improvement in oxidative capacity after a
sity of exercise; in addition, glycogen depletion is dependent on the training phase with low or empty glycogen
total amount of glycogen that can be stored and on how much stores, it has not yet been conclusively shown
the stores are filled at the beginning of exercise [8]. In the case whether this has medium-term or long-term
of intense endurance exercise within the range of the anaerobic consequences for competition performance
threshold, the energy that is stored in fully replenished glyco- [14, 16]. Training with low or empty glycogen
gen stores is sufficient for an exercise duration of approx. 75–90 stores may negatively affect performance by
minutes; incompletely filled glycogen stores are associated with a downregulating glucose transporters (GLUT-
correspondingly lower exercise duration [8, 11, 13]. 4) [17]. However, in the case of highly intense
Therefore, athletes who are training or competing on a regular basis endurance competitions, it is not possible to
should consider a sufficient amount of carbohydrates in their diet. succeed without carbohydrates as an energy
source; furthermore, regarding training peri-
♦ Table 1 shows differences in the amount of carbohydrate intake odization, the optimal timing to increase the
as a function of duration of training and exercise intensity, pub- amount of carbohydrate intake again has not
lished by the American College of Sports Medicine (ACSM) [1]. been established [1, 7, 14].
The exact amount of carbohydrates to improve performance in
different types of sports is still under debate [1, 6, 7, 14]. Par- Also the glycemic index is relevant with re-
ticularly when looking at different carbohydrate regimes during gard to the metabolic effects of a carbohy-
Ernaehrungs Umschau international | 11/2019 229
Peer Review | Position Paper
drate-rich diet in sports. The glycemic index describes the increase Nutrition on the day of competition
in blood glucose after the intake of carbohydrate containing meals It is recommended that endurance athletes
compared to the intake of a standard comparative food, such as should consume a carbohydrate-rich meal
white bread or glucose solution. In addition to the increase in (1–4 g carbohydrate/kg body weight, depend-
blood glucose, the postprandial increase in insulin levels is also ing on the duration and intensity) 2–3 hours
dependent on the glycemic index [20]. before a competition when exercise duration
The blood insulin level plays a key role in the regulation of car- exceeds 60 minutes [1]. This replenishes gly-
bohydrate oxidation versus fat oxidation [21]. A high glycemic cogen stores in the muscles and particularly
index is associated with a high postprandial insulin level which in in the liver, which could already show a sig-
turn leads to a lower fat oxidation [22, 23]. This association has nificant overnight reduction in glycogen levels
also been demonstrated in athletes during physical exercise [24]. [7]. Many albeit not all studies have demon-
However, whether carbohydrates with a low glycemic index can strated that a carbohydrate-rich meal prior to
also improve endurance capacity following training is currently exercise leads to an improvement in perfor-
under debate [25, 26]. mance [1].
The recommendation to consume the pre-ex-
Carbohydrates before competition ercise meal 2–3 hours before the start of com-
If the competition lasts less than 90 minutes, no change in the petition is based on the fact that by then the
daily intake regime shown in ♦ Table 1 is currently recommended feeling of fullness is reduced and the postpran-
[1, 23]. If the competition lasts more than 90 minutes, an increase dial hormonal response has largely returned
in carbohydrate intake in the days before competition has often to baseline. Following a carbohydrate-rich
shown to improve performance [27]. pre-exercise meal, metabolism of carbohy-
Strategies to further increase glycogen stores are known as car- drates is increased and fat oxidation is simul-
bohydrate loading or “supercompensation”. Currently, carbohy- taneously decreased because lipolysis and fat
drate loading can be recommended for a competition duration of oxidation are already inhibited by relatively
more than 90 minutes. small amounts of insulin in the blood. How-
The method of carbohydrate loading that is most common at the ever, the higher proportion of carbohydrates
moment involves a relatively high increase in carbohydrate intake that is now being metabolized is fully com-
of 10–12 g carbohydrate/kg of body weight per day (kg body pensated by the higher amount of carbohy-
weight/d) for a period of 36–48 hours prior to competition. This drates ingested by the carbohydrate-rich meal.
can further increase glycogen concentration in the muscles by Therefore, although carbohydrate oxidation is
approx. 10–15% and allows carbohydrate oxidation to be main- increased this is not associated with a quicker
tained longer during endurance exercise. Another method for car- depletion of glycogen stores. In the case of a
bohydrate loading consists in increasing carbohydrate intake in very short pre-exercise interval of less than
the week prior to a competition (e.g. 9–10 g carbohydrate/kg 60–90 minutes, blood glucose concentrations,
body weight/d) with simultaneous reduction in the extent and and particularly insulin concentration remain
intensity of training. relatively high at the start of exercise. This in-
A further method involves intensive, glycogen-depleting endur- duces a pronounced increase in carbohydrate
ance exercise 72 hours prior to the competition. The prior exercise metabolism in skeletal muscles that can be
is intended to upregulate the activity of GLUT-4-transporters and desirable for shorter, more intensive periods
glycogen synthase, which should also lead to a supramaximal of exercise within the range of the anaerobic
filling of glycogen stores in the subsequent days until competition threshold. For long endurance distances in
when further supported by a carbohydrate-rich diet (e.g. 9–10 g a rather moderate intensity range (60–70%
carbohydrate/kg body weight/d). VO 1
2max ), however, a higher metabolic pro-
portion of fat is preferable, as this also pro-
It is not advised to test out different methods for carbohydrate load- tects the glycogen stores. For this reason, the
ing before an important competition. Not all athletes can tolerate interval between the intake of food and the
very large quantities of carbohydrates and it is not advisable to risk start of the competition should be selected in
compromising performance in important competitions due to gas- such a way that the initial digestive phase is
trointestinal problems. It is often stated that athletes should train completed and the insulin concentration has
the gastrointestinal system in order to deal with a high carbohy- returned largely to the fasting range.
drate intake. However, further research is required to investigate
the extent to which this is necessary, feasible and tolerable [28].
1 VO max: maximal O uptake from inhaled air per unit of
2 2
time during maximum exertion.
Ernaehrungs Umschau international | 11/2019
230
The glycemic index of the meal eaten prior as a “final reserve” towards the end of a high-intensity exercise
to exercise can also affect substrate oxida- [27, 32, 33].
tion during exercise. Studies have shown
that a pre-exercise meal with a low glycemic For practical reasons, during exercise, carbohydrates are usually
index leads to increased fat oxidation during consumed in the form of drinks. It is currently recommended
the subsequent exercise [24, 29]. This means that, depending on the intensity of exercise, individual tolerance
that due to lower insulin concentration, fatty and climatic conditions, 150–350 ml of a drink with a carbo-
acids are metabolized preferentially over car- hydrate concentration of approx. 6% should be drunk every 15
bohydrates at the same intensity of exercise. minutes for a duration of more than 60 minutes [34].
A possible advantage of this would be that the Frequently, athletes ask whether certain forms of carbohydrate
glycogen stores are conserved during longer administration (e.g. drink, bar, or gel) have different effects on the
periods of exercise requiring endurance due to speed of carbohydrate oxidation during exercise. Although car-
the relatively higher proportion of fatty acids bohydrates are certainly available more quickly in liquid form,
used in energy production. it does not seem to play a role during prolonged exercise per-
However, the statements that have been made formance in which dosage form the carbohydrates are supplied.
regarding the effects and significance of the Here, athletes can follow their personal preferences [35]. However,
glycemic index in the pre-exercise phase are it should be noted that extra care must be taken to ensure a suf-
contradictory. Depending on the studies in- ficient intake of fluids so that the passage through the stomach is
cluded and the test algorithm chosen, the not delayed and the osmotic load is not too high.
meta-analysis by Heung-Sang et al. comes to
the conclusion that a low glycemic index in The oxidation rate of exogenously supplied glucose during ex-
pre-exercise meal provides a performance ad- ercise is approx. 1–1.2 g/min and cannot be further increased
vantage [26], whereas the meta-analysis by through a higher glucose or maltodextrin intake. During sub-
Burdon et al. showed no significant difference maximal exercise, the limiting factor is the absorption in the small
[25]. intestine rather than the gastric emptying rate [28]. In fact, glu-
cose transport proteins in the small intestine have a capacity limit.
However, studies have shown that different carbohydrates taken
up by different carrier systems lead to increased absorption and
Carbohydrate intake during thus increased carbohydrate oxidation. Therefore, a combination
physical exercise of glucose, fructose and sucrose, respectively, increased the oxida-
tion rate to values of 1.5-1.7 g/minute [11, 23].
General recommendations
In most studies, continuous carbohydrate From the current literature, it can be deduced that the use of dif-
intake during intensive, long-lasting exercise ferent carbohydrates with different transport mechanisms could
maintained the oxidation of carbohydrates be useful, especially in the case of extremely intensive endurance
and thus prevented hypoglycemia and in turn stress over 2.5 hours [36, 37]. However, it has to be pointed out
prevented termination of exercise [30]. In ad- that athletes often cannot tolerate such large amounts of carbo-
dition, the immediate involvement of orally hydrates during physical exercise. It is often reported that the in-
administered carbohydrates in energy metab- take of large amounts of carbohydrates can be trained; this must
olism during exercise was demonstrated using be tested individually [28]. Since many preparations containing
labeled glucose. Furthermore, systematic re- carbohydrate mixtures contain fructose, fructose intolerance
views and meta-analyses have confirmed that must be excluded in advance, otherwise negative effects on per-
the exercise time that can be achieved is ex- formance can be expected.
tended significantly by continuous carbohy-
drate intake during exercise [1, 6]. In recent years, there has been much speculation as to whether
Extended performance through carbohydrate the additional administration of protein in the form of a carbohy-
intake is attributable, among other factors, drate-protein mixture can improve performance even further. The
to conservation of glycogen in the muscles, number of studies on this is rather sparse [38]. However, there is
conservation of hepatic glycogen stores, the a broad consensus that when glucose intake is adequate, the ad-
prevention of hypoglycemia, and the main- dition of extra protein does not have any performance-enhancing
tenance of a high energy flow rate [1, 7, 8, effect [13]. Some studies demonstrated that the intake of a carbo-
31]. The conservation of glycogen stores in hydrate-protein mixture led to a reduction in the release of muscle
the liver is particularly important during ex- enzymes (e.g. creatine kinase) and decreased muscle fatigue [38,
ercise involving intensive “final spurts”, as 39]. Even so, the relevance of these findings in terms of endurance
these hepatic glycogen stores can still be used and success of training is uncertain. Therefore, when carbohy-
Ernaehrungs Umschau international | 11/2019 231
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